Thioformyldiphenylthiophosphinates and poly-alpha-olefin compositions containing them



United States Patent 3,419,523 THIOFORMYLDIPHENYLTHIOPHOSPHINATES ANDPOLY-a-OLEFIN COMPOSITIONS CON- TAINING THEM Sheldon Herbstman, SpringValley, N.Y., assignor to Stautfer Chemical Company, New York, N.Y., acorporation of Delaware No Drawing. Original application Oct. 23, 1965,Ser. No. 504,190. Divided and this application Dec. 5, 1967, Ser. No.705,253

14 Claims. (Cl. 260-4585) ABSTRACT OF THE DISCLOSURE Solid lightresistant compositions comprising an a-olefin polymer of from 2 to 10carbon atoms and a thioformyldiphenylthiophosphinate stabilizer of theformula:

wherein R is selected from the class consisting of alkyl of from 1 to 20carbon atoms, phenyl, naphthyl and benzyl, R is an aromatic hydrocarbonradical selected from the classco'nsisting of phenyl, naphthyl,chlorophenyl, lower alkylated phenyl and lower alkoxyphenyl and Z is achalcogen' selected from the class consisting of sulfur andoxygen. Heatresistant compositions are also encompassed by the addition of a dialkyl3,3'-thiodipropionate, each alkyl group having from 4 to 18 carbonatoms.

This application is a division of application No. 504,- 190, filed Oct.23, 1965.

This invention relates to organophosphorus esters and in particular tothioformyldiphenylthiophosphinates. The invention is likewise concernedwith the use of the aforenamed materials as light and heat stabilizersfor poly-aolefin compositions.

As used herein dithioformyldiphenylphosphinates includethioformyldiphenylphosphinothioate and thioformyldiphenyldithioa-tes.

It is known that plastics and polymeric materials generally undergodegradation in the presence of light and/or heat. Especially sensitiveto these agencies are some of the recently developed synthetic resinsand in this connection mention is made of the poly-ot-olefins such aspolyethylene, polypropylene and the like. For instance, isotacticpolypropylene undergoes air oxidation at the relatively mild temperatureof 125. Even more sensitive are polypropylene fibers which lose about50% of their tensile strength when exposed for fifty hours in acirculating air oven at 125 C. At the end of 100 hours, the fibers aretransformed into a powdery material.

Isotactic polypropylene is also unusually sensitive to ultraviolet lightas shown by an appreciable lessening of tensile strength after fiftyhours exposure to this damaging actinic radiation. In order to increasethe life of plastics and polymers, it is the practice to incorporatetherein certain substances, usually referred to as ultravioletabsorbers, which are capable of absorbing the incident actinic radiationthereby protecting the plastic substrate from deterioration. It is alsothe practice to use other types of additives which are capable ofpreventing breakdown of the plastic due to air oxidation at elevatedtemperatures. These latter additives are customarily designated as heatstabilizers and commonly embrace a phenolic type of structure.

It has now been discovered that certainthioformyldiphenylthiophosphinates are effective in protectingpoly-aolefins against the deleterious effects of both light and heat andthe provision of such compounds constitutes the primary purpose andobject of the present invention.

Patented Dec. 31, 1968 Another important object of the invention is toprovide poly-ot-olefin compositions stabilized with the above namedcompounds. Other objects and purposes will become manifest hereinafter.

The thioformyldiphenylthiophosphinates. of the invention whichconstitute a hitherto unknown class of organophosphorus esters can bedepicted by the following formula:

wherein R is alkyl of from 1 to 20 carbon atoms, e.g., methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, sec.- butyl, n-pentyl,isopentyl, n-hexyl, isohexyl, n-heptyl, noctyl, isooctyl, n-nonyl,n-decyl, n-undecyl, n-dodecyl, tridecyl, tetradecyl, pentadecyl,hexadecyl, heptadecyl, octadecyl, nondecyl, etc., and aromatichydrocarbon radical such as phenyl, naphthyl and the like, or an aralkylradical such as benzyl; R is an aromatic hydrocarbon radical such asphenyl, or substituted phenyl as illustrated by halophenyl,chlorophenyl, lower alkylated phenyl, lower alkoxy phenyl and the likeor naphthyl, and Z is a chalcogen as exemplified by sulfur and oxygen.Specific compounds falling within the ambit of the above depictedformula include the following:

i (H) P-SCSCd-Igiso The thioformyldiphenylthiophosphinates of theinvention can be realized by reacting a thioformyl halide such asmethylthioformyl chloride with a diarylphosphinothioate or adiarylphosphinodithioate salt in accordance with the chemical equationset forth below:

(R )7PSM+RSQ c1- R')1P-scsR+Mo1 wherein R R and Z have the values aspreviously assigned and M is a metallic cation such as sodium,potassium, lithium, ammonium, substituted ammonium or silver. Inpreparing the new organophosphorus esters of the invention, I haveascertained that generally excellent results ensue by heating thethioformyl halide with the alkali metal or ammonium salt of therequisite diarylthiophosphinic acid with or without a solvent andthereby isolating the thioformyldiarylthiophosphinate ester from theby-product of alkali metal or ammonium halide. An especially convenientmeans for carrying out the reaction is to reflux the components in thepresence of a relatively inert organic solvent such as the lowerketones, alcohols, saturated aliphatic hydrocarbons, aromatichydrocarbons or their chlorinated derivatives or the liquid saturatedaliphatic ethers. After removing the alkali metal halide byproduct anddistilling off the solvent, the residual thioformyldiarylthiophosphinateester can be isolated by employing the usual techniques available to theskilled organic chemist such as crystallization, distillation,sublimation and the like.

The ultraviolet and heat stabilizers contemplated by the invention canbe blended or incorporated into the poly-a-olefin compositions by any ofthe conventional methods commonly used for mixing such materials withresins and plastics. A typical procedure comprises milling on heatedrolls, although deposition from solvents and dry blending are other wellknown techniques.

The poly-u-olefin compositions stabilized in accordance with theinvention exhibit an extended life expectancy and are much more usefuland practical than unstabilized polya-olefins and moreover possess awide diversity of uses including out-of-door installations underprolonged exposure to sunlight and the elements. The poly-a-olefinsstabilized as contemplated herein can be cast, extruded, rolled ormolded into sheets, rods, tubes, piping, filaments and other shapedarticles, including sheets or films ranging from 0.5 to mils inthickness. The polymer compositions of my invention can be applied ascoatings to paper, cloth, wire, metal foil and are suitable for themanufacture of synthetic fibers and fabrics. Although the quantity ofstabilizer is not particularly critical, it is recommended that theconcentration based on the weight of the polymer be maintained in therange of 0.01 to about 5.0%.

The organic thiophosphorus compounds as described herein are suitablefor stabilizing a wide variety of solid poly-u-olefin compositionsagainst deterioration resulting from exposure to actinic radiation. Inthis connection, mention is made of any of the normally solid polymersderived from the polymerization of a-mono-olefinic aliphatichydrocarbons containing from two to ten carbon atoms. Typicalpoly-a-olefins include polyethylene, polypropylene,poly(3-methylbutene-l), poly(4-methylpentene-l poly(pentene-1), poly3,3-dimethylbutene-l poly(4,4 dirnethylbutene 1), poly(octene 1),p'oly(decene l), and the like. I have ascertained that the organicthiophosphorus stabilizers of the invention are particularly elfectivefor preventing photodegradation by ultraviolet light or sunlight of thehighly crystalline polyolefins such as isotactic polypropylene.Isotactic polypropylene is a stereo-regular polymer wherein themonomeric units are linked predominantly end-to-end rather than the morecommon arrangement consisting of a distribution of linear andcross-linked units. Moreover, the substituents attached to the chain aresystematically disposed in a configuration which tends to promote anorderly and close alignment of the molecules. Such stereo-regularpolymers exhibit a high degree of crystallinity and are much superior inphysical properties to amorphous polymers having a random distributionof monomeric units. For a fuller description of crystalline polymers,reference is made to the Scientific America, 197 No. 3, pp. 98-104(1957); 205 No.2, pp. 3341 (1961).

Although the molecular weight of p'oly-a-olefins varies over widelimits, the UV. stabilizer compounds of the invention are not restrictedto any particular molecular weight range and in fact it has been myfinding that excellent protection can be achieved with poly-a-olefinsranging in molecular weight from about 15,000 to about 20,000. Moreover,the so-called poly-a-olefin Waxes are likewise susceptible to UV.stabilization by means of the compounds of the invention.

The following examples illustrate the procedures for preparing thethioformyldiarylthiophosphinates and to poly-a-olefin compositionscontaining such compounds but it is to be understood that the inclusionof such examples is not to be taken as limiting or otherwise imposingany restriction on the invention and it is to be further understood thatvariations in practicing the same without departing from the scope orspirit thereof will be apparent to those skilled in the art to which thesaid invention pertains.

PREPARATION OF THE COMPOUNDS Examplel.Methylthioformyldiphenylphosphinodithioate 6.8 g. (0.025 mole) sodiumdiphenylphosphinodithioate was dissolved in 100 ml. of acetone to whichwas added slowly 2.76 g. (0.025 mole) of methylthioformylchloridedissolved in 25 ml. of acetone. The reaction mixture was refluxed fortwo hours, during which time sodium chlo- Example2.Phenylthioformyldiphenylphosphinodithioate White crystals; M.P. 62.

Example 3.n-Propylthioformyldipheny'lphosphinodithioate s T llQ-P-S-CSCaHv Yellow oil, B.P. 52/ 1.0 mm.

Example 4.n-Octylthioformyldiphenylphosphinodithioate Yellow oil,nondistillable.

POLYMERIC COMPOSITIONS CONTAINING THE COMPOUNDS Example A dry blendconsisting of 0.5% by weight of methylthioformyldiphenylphosphinodithioate and 50 g. of iso tactic polypropylene wassubjected to compression molding in the usual manner at a temperature of400 F. for six minutes at 2000 psi. The blended polymer was compressionmolded or extruded into a 25 mil sheet and thereafter cut into squaresamples measuring 2 inches on the side. A like sample containing nostabilizer was also prepared and tested. The samples were then exposedin a Xenon Arc Weatherometer operating at 6000 watts. The water cyclewas adjusted whereby each sample was subjected to 18 minutes of waterspray and 102 minutes of dry exposure for each two hours of exposure.Exposure damage to the samples of polypropylene was assessed withrespect to change of strutcural strength.

After a period of exposure in excess of 850 hours, the test sheet ofpolypropylene showed no signs of brittleness to 180 fiexure test. Norwas there any evidence at this time of any surface crazing or anycoloration or staining. A blank specimen of unstabilized polypropylenewhich was exposed concurrently with the stabilized product failed theflexure test after 250 to 300 hours exposure time.

The Weatherometer as used in compiling the data and tests describedherein is identified as a 6000 Watt Xenon Arc Weatherometer Model 60 W.

The polypropylene resin as used in the above described example is anunstabilized general purpose, high molecular weight polypropylene of theisotactic or crystalline type. Typically, it has a melt index of 4 at230 C. and a specific gravity of 0.905. The resin was purchased underthe trade name Profax and further identified as number 6501, typeP-02004 and is supplied in the form of natural flakes. We have also usedother comercially available grades of unstabilized isotacticpolypropylene resin, and in this connection, mention is made ofunstabilized Avisun polypropylene and unstabilized Shell polypropylene.The results obtained in using the various grades and types ofpolypropylene were in general agreement.

As previously pointed out elsewhere herein, thethioformyldiphenylthiophosphinates of the invention are not onlyeffective as light and ultraviolet stabilizers but are also capable ofalfording protection of the polymeric substrate against heatdegradation. In this connection, an especially interesting and highlyvaluable property of the compounds of the invention is that they arecapable of being synergized with esters of thiodipropionic acid. Although this well-known synergist is capable of emphasizing or amplifyingthe stabilization of antioxidants generally one class of stabilizerswhich is an exception to the rule are the organophosphorus derivatives.However, the particular organophosphorus compounds of the invention aresurprisingly susceptible to being synergized by thiodipropionic acidesters and this constitutes a new and valuable asset of the invention.The amount of the synergist required to complement the stabilizingproperties of the thioformyl diphenylthiophosphinate lies within theusual range, that is to say, from about 0 .01% to about 5.0% by weightbased on the weight of the polymer; I have ascertained, for instance,that a concentration of 0.2% of the thiodipropionic acid ester iseminently satisfactory. A typical procedure for combining thethioformyldiphenylthiophosphinate stabilizers of the invention and thethiodipropionic acid ester synergist is set forth in the followingexample.

Example 6 10.0 g. powdered polypropylene resin containing 0.5 ofmethylthioformyldiphenylphosphinodithioate and 0.2% ofdilaurylthiopropionate was placed on the center of a 6" x 6" stainlesssteel plate. A similar steel plate was then placed on top of the powderwhile exerting a slight downward pressure. The assembly was placed inthe center of the lower platen of a hydraulic press which was previouslyheated to 400 F. The lower platen of the press was raised until bothplatens contacted the upper and lower 6" x 6" stainless steel plates.The powder sample was allowed to warm up for about 4 minutes or untilfusion of the resin occurred. As the pile of resin began to melt, thelower platen of the press was raised slightly to ensure that bothplatens contacted the steel plates en closing the sample. After about 4minutes or when the fusion of the resin occurred, the lower platen wasraised to a one ton load and so maintained for 2 minutes. The drainvalve was then opened to vent off steam, after which cold water wasadmitted to cool the platens and plates to 50 F. The molded sheet ofresin was approximately 25- 30 mils thick.

1" discs were cut from the molded sheet and placed in petri dishes andthen exposed to a temperature of C. in a forced draft oven. The samplecontaining the methylthioformyl diphenylphosphinodithioate survived anexposure time in the neighborhood of 150 hours before exhibiting signsof enbrittlement.

The mixture of powdered propylene resin and antioxidant as used in theabove described procedure was prepared by intimately mingling thepropylene resin and antioxidant in a Waring Blendor until a homogeneousmixture of the components was obtained.

The polypropylene resin as used in the example above was identical withthe resin which was defined and described under Example 5.

Diesters of 3,3-thiodipropionic acid which are used in combination withthe stabilizer components of the invention have the following formula:

S(CH -CH -COOR) wherein R is an alkyl radical having at least 4 andgenerally 4 to 20 carbon atoms with 8 to 18 carbon atoms beingpreferred. An especially efficacious ester has 12 carbon atoms per Rsubstituent, namely 3,3-thiodipropionic acid dilauryl ester. However,any diester of 3,3'-thiodi propionic acid described above can beemployed in the present stabilizer combination, wherein R is butyl,amyl, heXyl, heptyl, octyl, nonyl, decyl, tridecyl, tetradecyl, and thelike.

I claim:

1. A solid poly-zx-olefin composition having improved stability towardheat and light degradation which comprises an a-olefin polymer formed bythe polymerization of an a-monoolefinic aliphatic hydrocarbon havingfrom 2 to carbon atoms and a stabilizing quantity of athioformyldiphenylthiophosphinate of the following formula:

wherein R is selected from the class consisting of alkyl of from 1 tocarbon attoms, phenyl, naphthyl and benzyl, R is an aromatic hydrocarbonradical selected from the class consisting of phenyl, naphthyl,chlorophenyl, lower alkylated phenyl and lower alkoxyphenyl and Z is achalcogen selected from the class consisting of sulfur and oxygen, and adialkyl 3,3-thiodipropionate, each alkyl group of which has from 4 to 18carbon atoms.

2. A composition according to claim 1 wherein the solid poly-a-olefin ispolypropylene.

3. A composition according to claim 1 wherein the dialkyl3,3-thiodipropionate is dilauryl 3,3-thiodipropionate.

4. A solid poly-wolefin composition according to claim 1 having improvedstability toward heat and light degradation which comprises solidpolypropylene and a stabilizing quantity of athioformyldiphenylthiophosphinate of the following formula:

T ll

wherein R is selected from the class consisting of alkyl of from 1 to 20carbon atoms, phenyl, naphthyl and benzyl, R is an aromatic hydrocarbonradical selected from the class consisting of phenyl, naphthyl,chlorophenyl, lower alkylated phenyl and lower alkoxylphenyl and Z is achalcogen selected from the class consisting of sulfur and oxygen, and adialkyl 3,3'-thiodipropionate, each alkyl group of which has from 4 to18 carbon atoms.

5. A solid poly-a-olefin composition according to claim 1 havingimproved stability toward heat and light degradiation which comprisessolid polypropylene and about 0.01% to about 5.0% based on thepolypropylene of methylthioformyldiphenylphosphinodithioate and about0.01% to about 5.0% of dilauryl 3,3-thiodipropionate.

6. A solid poly-aolefin composition according to claim 1 having improvedstability toward heat and light degradiation which comprises solidpolypropylene and about 0.01% to about 5.0% based on the polypropyleneof phenylthioformyldiphenylphosphinodithioate and about 0.01% to about5.0% of dilauryl 3,3'-thiodipropionate.

7. A solid poly-a-olefin composition according to claim 1 havingimproved stability toward heat and light degradation which comprisessolid polypropylene and about 0.01% to about 5.0% based on thepolypropylene of npropylthioformyldiphenylphosphinodithioate and about0.01% to about 5.0% of dilauryl 3,3-thiodipropionate.

8. A solid poly-a-olefin composition according to claim 1 havingimproved stability toward heat and light degradation which comprisessolid polypropylene and about 0.01% to about 5.0% based on thepolypropylene of noctylthioformyldiphenylphosphinodithioate and about0.01% to about 5.0% of dilauryl 3,3-thiodipropionate.

9. A solid light resistant composition which comprises an a-olefinpolymer formed by the polymerization of an oc-IIIOIIOOlGfiHiC aliphatichydrocarbon having from 2 to 10 carbon atoms and a stabilizing quantityof a thioformyldiphenylthiophosphinate of the following formula:

wherein R is selected from the class consisting of alkyl of from 1 to 20carbon atoms, phenyl, naphthyl and benzyl, R is an aromatic hydrocarbonradical selected from the class consisting of phenyl, naphthyl,chlorophenyl, lower alkylated phenyl and lower alkoxylphenyl and Z is achalcogen selected from the class consisting of sulfur and oxygen.

10. A solid light resistant composition according to claim 9 whichcomprises solid polypropylene and a stabilizing quantity of athioformyldiphenylthiophosphinate of the following formula:

wherein R is selected from the class consisting of alkyl of from 1 to 20carbon atoms, phenyl, naphthyl and benzyl, R is an aromatic hydrocarbonradical selected from the class consisting of phenyl, naphthyl,chlorophenyl, lower alkylated phenyl and lower alkoxylphenyl and Z is achalogen selected from the class consisting of sulfur and oxygen.

11. A solid light resistant composition according to claim 9 whichcomprises solid polypropylene and about 0.01% to about 5.0% based on thepolypropylene of methylthioformyldiphenylphosphinodithioate.

12. A solid light resistant composition according to claim 9 whichcomprises solid polypropylene and about 0.01% to about 5.0% based on thepolypropylene of phenylthioformyldiphenylphosphinodithioate.

13. A solid light resistant composition according to claim 9 whichcomprises solid polypropylene and about 0.01% to about 5.0% based on thepolypropylene of npropylthioformyldiphenylphosphinodithioate.

14. A solid light resistant composition according to claim 9 whichcomprises solid polypropylene and about 0.01% to about 5.0% based on thepolypropylene of noctylthioformyldiphenylphosphinodithioate.

References Cited UNITED STATES PATENTS 2,545,158 3/1951 McDermott26045.7

DONALD E. CZAJ A, Primary Examiner.

V. P. HOKE, Assistant Examiner.

US. Cl. X.R. 260 .7

